The invention relates to a honing tool for machining cylindrical bores.
Honing is a cutting process using geometrically undefined cutting edges, in which a honing tool performs a cutting movement consisting of two components and there is constant surface contact between one or more cutting material bodies of the honing tool and the internal bore surface to be machined. The kinematics of an expandable honing tool are characterized by superimposition of a rotary movement, of a stroke movement running in the axial direction of the bore and of an infeed movement which leads to a change in the effective diameter of the honing tool. A surface structure with intersecting finishing marks is obtained on the internal bore surface. Surfaces finish-machined by honing can satisfy extremely high requirements with regard to dimensional and geometrical tolerances, and so many highly loaded sliding surfaces in engines or engine components, e.g. cylinder faces in engine blocks or internal bore surfaces in housings of injection pumps, are machined by honing.
Especially during the machining of bores having relatively small diameters, for example a diameter of around 15 mm or less, honing tools which have a tubular tool body are used, the tool body being fastened with one end section in a tool shank and having at the opposite end section a cutting region having at least one honing-stick accommodating opening which is continuous from the interior of the tool body to the outside and is intended for accommodating a honing stick. The tool body serves in this case as a holder for one or more honing sticks and at the same time as a guide for an infeed rod which is used for the radial infeed of the honing sticks. The tool shank serves on the one hand for accommodating the tool body and on the other hand for fastening the honing tool to the work spindle of a honing machine.
The dimensions of the honing-stick accommodating opening, which is rectangular as a rule, and the corresponding cross-sectional dimensions of the honing stick are matched to one another in such a way that the honing stick is accommodated in a radially movable manner, and essentially free of play in the circumferential direction of the tool body, between boundary surfaces of the honing-stick accommodating opening. As a rule, it is attempted in this case to realize a sliding fit by exact machining of the boundary surfaces of the honing-stick accommodating opening and the corresponding side surfaces of the honing stick, such that the honing stick can only just be inserted manually into the honing-stick accommodating opening and is held there by static friction forces between side surfaces of the honing stick and the adjoining boundary surfaces of the honing-stick accommodating opening.
The inner side of the honing stick, which inner side projects into the interior of the tool body, has as a rule a sloping surface which interacts with a sloping surface at the end of the infeed rod like a wedge drive in such a way that an axial displacement of the infeed rod to that end of the tool body which is remote from the spindle displaces the honing stick radially outwards. DE 299 21 053 U1 shows examples of such honing tools.
Honing tools of this type are very reliable and guarantee the best machining results. After a prolonged service life, however, damage to the honing stick can be observed every now and then, this damage partly being recognized as one-sided wear of the cutting layer. In individual cases, it was also observed after a prolonged service life that honing sticks can jam in the honing-stick opening. A situation can also occur in which honing sticks fall out of the honing-stick accommodating opening after a prolonged service life when the honing tool is withdrawn from the machined bore. In order to prevent the honing sticks from falling out of honing tools, what are referred to as stick catch bushes are used in some cases. These are essentially sleeve-shaped components which are guided in a slidable manner on the tool body above the cutting region and are displaced, on account of their dead weight, over the cutting region with the honing sticks when the honing tool is withdrawn from the bore. This prevents honing sticks from falling out and any possible difficulties are avoided when inserting the honing tool into the next bore to be machined.